All the Duo-Art pulleys I have seen are marked with a direction arrow.
This is the direction that the pump is driven which tightens the pulley.
To remove it turn it the opposite way.

I would not use the board clamping method if the spider arm is held
with wood screws unless they are holding really well. Machine screws
through the boards will hold against the shock of bashing the pulley.
Be sure to tighten the nuts if they are loose.

The pulleys can be quite stuck so a shock impulse is likely to be
better than a constant force. Soaking with penetrating oil for
a couple of days will help with a really stubborn pulley.

I have seen a couple of pulleys that were locked with a tapered pin.
Look carefully for and remove such a pin before attempting to remove
the pulley. If it just won't budge there may be a hard-to-find pin.

Finally, do not bash really hard on the pulley. It is cast iron and
can break and be difficult to braze or weld without warping.

Spencer Chase
Northern California